From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan: fix random seed generation for tag-based mode There are two issues with assigning random percpu seeds right now: 1. We use for_each_possible_cpu() to iterate over cpus, but cpumask is not set up yet at the moment of kasan_init(), and thus we only set the seed for cpu #0. 2. A call to get_random_u32() always returns the same number and produces a message in dmesg, since the random subsystem is not yet initialized. Fix 1 by calling kasan_init_tags() after cpumask is set up. Fix 2 by using get_cycles() instead of get_random_u32(). This gives us lower quality random numbers, but it's good enough, as KASAN is meant to be used as a debugging tool and not a mitigation. Link: http://lkml.kernel.org/r/1f815cc914b61f3516ed4cc9bfd9eeca9bd5d9de.1550677973.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/arch/arm64/kernel/setup.c~kasan-fix-random-seed-generation-for-tag-based-mode +++ a/arch/arm64/kernel/setup.c @@ -339,6 +339,9 @@ void __init setup_arch(char **cmdline_p) smp_init_cpus(); smp_build_mpidr_hash(); + /* Init percpu seeds for random tags after cpus are set up. */ + kasan_init_tags(); + #ifdef CONFIG_ARM64_SW_TTBR0_PAN /* * Make sure init_thread_info.ttbr0 always generates translation --- a/arch/arm64/mm/kasan_init.c~kasan-fix-random-seed-generation-for-tag-based-mode +++ a/arch/arm64/mm/kasan_init.c @@ -252,8 +252,6 @@ void __init kasan_init(void) memset(kasan_early_shadow_page, KASAN_SHADOW_INIT, PAGE_SIZE); cpu_replace_ttbr1(lm_alias(swapper_pg_dir)); - kasan_init_tags(); - /* At this point kasan is fully initialized. Enable error messages */ init_task.kasan_depth = 0; pr_info("KernelAddressSanitizer initialized\n"); --- a/mm/kasan/tags.c~kasan-fix-random-seed-generation-for-tag-based-mode +++ a/mm/kasan/tags.c @@ -46,7 +46,7 @@ void kasan_init_tags(void) int cpu; for_each_possible_cpu(cpu) - per_cpu(prng_state, cpu) = get_random_u32(); + per_cpu(prng_state, cpu) = (u32)get_cycles(); } /* _
